1. Field of the Invention
The present invention relates to a continuous image estimation method and, more particularly, to a continuous binary or dither image estimation method for estimating an original continuous image excellently a binary or dither image displayed in pseudo-halftone.
2. Description of the Prior Art
Most output units practised at present such as displays or printers cannot display images other than in binary values, i.e., in white and black colors.
As the method of falsely expressing a halftone by the use of such output unit, there is known a density pattern method (or a luminance pattern method) or a dither method.
Both the density pattern method and the dither method are a kind of areal gradation method and express a continuous image by changing the number of dots to be recorded in a constant area (i.e., matrix).
The density pattern method is one for recording a portion of an original corresponding to one picture element with a plurality of dots by using a threshold matrix, as shown in FIG. 25(B), and the dither method is one for recording the portion of the original corresponding to one picture element with one dot, as shown in FIG. 25(A) so that binary output data are obtained, respectively, as shown. These output data express a continuous image falsely in binary white and black values.
Now, if the continuous image (corresponding to the input data of FIG. 25) of an original could be estimated from the pseudo-continuous image thus made binary, a binary image having an excellent quality could advantageously be formed by a binary treatment using that pseudo-continuous tone image.
In the case of the density pattern image, the continuous image can be instantly restored if the arrangement of a pattern level is known. However, a resolution is low for the quantity of information.
On the contrary, the dither image has a higher resolution for the quantity of information than that of the density pattern image but is difficult to be returned to the original continuous image.
In case the continuous image is to be thus estimated, on the other hand, it is estimated without special consideration into the human visual characteristics and the kind of the image. As a result, the features of the image are not utilized so that the image quality cannot be sufficed. If the visual characteristics are also considered, the original continuous image can be copied better.
In case a picture element to be estimated has its density changing drastically as at an edge, on the other hand, the scanning aperture used is single to raise a defect that the edge cannot be restored to a satisfactory extent, even if the level of the continuous image is to be estimated by using one of sixteen kinds of scanning apertures. Since the human vision has a high power to discriminate the edge of an image, as is well known in the art, it recognizes the entirety of the reproduced image in the worse quality if the reproducibility of the edge is the more degraded.